Evaporative chemical evolution of natural waters at Yucca Mountain, Nevada

Abstract

The authors report results from experiments on the evaporative chemical evolution of the two major types of natural waters present at Yucca Mountain, Nevada. The first is represented by J13 well water, a dilute Na–HCO 3–CO 3 water similar to saturated horizons in volcanic tuffs across the western United States. The second is represented by Ca–C1–SO 4-rich pore water that has a higher dissolved ion content, from the unsaturated zone above the repository horizon. Data include anion and cation analysis and qualitative mineral identification for a series of open system experiments, with and without crushed tuff present, conducted at sub-boiling temperatures (75–85°C). This work is motivated by a need to characterize the chemistry of concentrated aqueous films that might form on engineered components at the potential high-level, nuclear-waste repository at Yucca Mountain, Nevada and lead to electrochemical corrosion. The experiments indicate the evolution of high pH, Na–HCO 3–CO 3 brines from J13-like waters and the evolution of near-neutral pH brines from the pore water compositions. The minerals recovered after complete evaporation of the J13 water alone experiments include amorphous silica, aragonite, calcite, halite, niter, thermonatrite and, possibly, gypsum, anhydrite and hectorite. Tachyhydrite and gypsum were observed to form in equivalent experiments with pore waters from the unsaturated zone.